Resonators exhibit resonance or resonant behavior at certain frequencies, called resonant frequencies. Oscillations in a resonator can be either electromagnetic or mechanical (including acoustic). Resonators can be used to either generate waves of specific frequencies or to select specific frequencies from a signal. A plasmonic resonator couples to plasmons, which are waves associated with electromagnetic fields and electron motion near the surface of a conducting or semiconducting material. The wavelength of plasmons is typically several times smaller than the wavelength of free-space electromagnetic radiation of similar frequency, and plasmonic resonators may therefore be comprised of relatively small structures as compared to a free-space wavelength at their resonant frequency. For optical frequencies, such structures are typically tens of nanometers in size, and referred to as nanostructures (e.g., nanocubes), but similar structures and plasmon resonators may be fabricated at larger scales to operate with lower frequency plasmons, e.g., in the infrared or THz ranges. One form of plasmonic resonator is comprised of a conductive nanostructure, such as a metallic nanocube, separated from a conductive substrate by a thin (few-nm at optical frequencies) dielectric (nonconducting) gap.